Multi-functional composite structures

ABSTRACT

A multi-functional composite system, the multi-functional composite system comprising a core, a plurality of structural composite fiber layers, a matrix material, a composite conductor assembly, the composite conductor assembly having one or more conductors disposed between two or more insulating layers, and an electric power source electronically coupled with said composite conductor assembly, the electric power source is configured to pass electric current through at least one of said one or more conductors.

This application is a Non-provisional of U.S. Patent Application No.62/007,375, filed Jun. 3, 2014, the contents of both incorporated hereinby reference.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support under Contract Number:FA8650-11-C-3110 awarded by United States Air Force. The government hascertain rights in the invention.

TECHNICAL FIELD

The present invention relates generally to wiring and wire harnesses.More particularly, the invention relates to apparatus and method for anaircraft conductor sandwich assembly embedded to an aircraft structuralmember.

BACKGROUND INFORMATION

Modern air vehicles contain many miles of electrical power and signalwiring. Wiring is costly to install, heavy, and vulnerable to damagefrom service (i.e., incorrectly routed near hot equipment and/or bundledtogether with other incompatible wire types such as soft wire layingadjacent to hard wire, etc.) and maintenance. Moreover, all wiredeteriorates in service due to environmental factors such as: extremeheat and cold temperature swings, humidity, salt damage associated withmarine environments, contamination by aircraft fluids (i.e., fuel, oil,hydraulic fluid, de-icing fluid, cleaning chemicals, toilet residue,galley spillage, etc.), as well as in-flight vibration causing chafingof wires rubbing against other wires or the structure of the aircraft.

The above-described electrical power and signal wiring are typicallyprovided through a wire harness (a.k.a. cable harness), which typicallybundles a collection of cables and/or wires that transmit informationalsignals (“signals”) or operating currents (“power”) from one point toanother. These wires and/or cables are often bound together to form aharness using, for example, clamps, cable ties, cable lacing, sleeves,electrical tape, conduit, a weave of extruded string, or a combinationthereof. On most aircraft, wire bundles contain many different wireswith several different types of insulation. Typically, wire bundles arecomposed of AC power cables, DC power cables, signal (circuitcontrolling) wires, and circuit ground wires. Also, there are bundlesthat carry power from different power sources (busses). These conditionsmake it extremely difficult to protect any circuit in such a bundle,where an insulation failure could result in an electrical problem thathas multiple power sources and current paths to feed it. A wide varietyof problems arise including shorting, arcing, or some other type ofdamage to a bundle with this mix of wires.

In addition to air vehicles (e.g., spacecraft, and aircraft), wireharnesses are used in automobiles, motorcycles, trains, ships, andboats. Indeed, vehicles typically contain many masses of wires that maystretch over several miles if fully extended. Binding the wires andcables into harnesses better secures them against the adverse effects ofvibrations, abrasions, and moisture. By constricting the wires into anon-flexing or semi-flexing bundle, usage of space is also increased,and the risk of a short circuit is greatly decreased. Similarly,installation time is decreased since an installer must install only asingle harness (as opposed to multiple loose wires). In certainsituations, the wires may be further bound into a flame-retardant sleevethat lowers the risk of electrical fires.

While the wire harnesses provide several advantages over loose wires andcables, wire harnesses still suffer from the above deficiencies. Forexample, in aviation, weight is a crucial factor and, as new militaryand civilian aircraft systems are developed, wire harnesses account forincreasingly larger mass fractions of the aircraft's total weight.Similarly, for new military and civilian aircraft platforms, there is acontinuous drive to simultaneously improve performance while reducingcosts. Another drawback of traditionally bound wire harnesses is theclutter and space inevitably occupied by the wire bundles. Furthermore,current aircraft development emphasizes electrical systems that enhancethe overall performance of the platform. This includes state-of-the-artsystems such as fly by wire, electro-hydraulic actuators, distributedsensor systems and high power payloads. With the increased demand onelectrical components have come increasingly complex installations andmaintenance. Current efforts to reduce the weight and complexity ofthese systems center on moving from cables to high-speed serialarchitectures, switching from hydraulic to electrical systems, anddistributed architectures. Not surprisingly, these efforts require anincreased emphasis on harness materials and design while significantlyreducing harness mass fraction; a task that cannot be accomplished withtraditional wire harnesses. Finally, traditional wire harnessingtechniques typically require specific components to secure harnessing(e.g., wires, and other conductors) along the length of a structure(e.g., fuselage, wing, etc.) and other features, such as holes orconduits, that facilitate passing the harnessing through a structure,such as ribs and bulkheads.

Thus, what is needed is an economical, lightweight wire harness capableof being embedded within or integrated with the structure and/or bodypanel of a vehicle. Embedment of these conductor systems in compositestructure during manufacture may signficantly reduce cost, weight,improve reliability, and most significantly, reducing the factor ofsafety (i.e., systems such as fly by wire (“FBW”) aircraft would benefitgreatly by allowing for improved redundancy and increased safety).

As will be discussed in greater detail below, such embedded wireharnesses may be facilitated using carbon nanotubes (“CNT”) material,carbon nano-filaments (“CNF”) material, fiber-reinforced plastic(“FRP”), fiber metal laminate (“FML”), metal deposited polyesternonwoven material (e.g., Nickel/Copper Polyester Nonwoven, and nickelchemical vapor deposition (“NiCVD”) coated fibers), or a combinationthereof. For example, one or more conductors (e.g., CNT, CNF, NiCVD,etc.) may be sandwiched between two or more insulating layers ofmaterial such that the conductor is electrically isolated and structuralloads can be passed through the conductor sandwich assembly (“CSA”). TheCSA may be incorporated either into or onto a composite structurewithout detrimental effect to the electrical and structural propertiesof the incorporated system.

SUMMARY

The present disclosure endeavors to provide an embedded conductor systemand/or wire harness enabled for use in aviation and other vehicles.

According to a first aspect of the present invention, a multi-functionalcomposite system comprises: a core; a plurality of structural compositefiber layers; a matrix material; a composite conductor assembly, thecomposite conductor assembly having one or more conductors disposedbetween two or more insulating layers, an electric power sourceelectronically coupled with said composite conductor assembly, theelectric power source is configured to pass electric current through atleast one of said one or more conductors.

According to a second aspect of the present invention, a heater assemblyfor embedment in a composite aircraft component comprises: a pluralityof conductors disposed between two or more sheets of insulating layers;an adhesive resin bonding the plurality of conductors and the two sheetsof insulating layers into a heater assembly such that (i) the conductorsare electrically isolated and (ii) structural loads can be passedthrough said heater assembly; and two or more electrical connectorselectronically coupled to one or more of said plurality of conductors,the two or more electrical connectors being configured such thatelectric current may be applied across said one or more of saidplurality of conductors causing said one or more of said plurality ofconductors function as a resistive load, thereby generating heat forde-icing or anti-icing the aircraft component.

According to a third aspect of the present invention, a method forheating an aircraft's load-bearing composite structure comprises thesteps of forming a composite conductor assembly having (i) one or moreconductors disposed between two sheets of insulating layers, and (ii) anadhesive resin bonding the one or more conductors and the two sheets ofinsulating layers such that the one or more conductors are electricallyisolated from each other and from any aircraft structural member, andsuch that structural loads can be passed through said conductor sandwichassembly; and bonding the composite conductor assembly to the aircraft'sload-bearing composite structure, the load-bearing composite structurehaving (i) a core, (ii) a plurality of structural composite fiberlayers, and (iii) a matrix material; and electrically coupling thecomposite conductor assembly with an electric power source, wherein atleast one of said one or more conductors is electrically coupled acrossthe electric power source's positive terminal and negative terminal tofunction as a resistive load, wherein the electric power source isconfigured to pass electric current through at least one of said one ormore conductors, and wherein said at least one of said one or moreconductors generates heat when electric current is passed through saidat least one of said one or more conductors.

In certain aspect, at least one of said one or more conductors may beelectrically coupled across the electric power source's positiveterminal and negative terminal to function as a resistive load. Incertain aspect, said at least one of said one or more conductorsgenerates heat when electric current may be passed through said at leastone of said one or more conductors. In certain aspect, the one or moreconductors are arranged to yield a wide area heater mat having apredetermined heat profile.

In certain aspect, the predetermined heat profile may be accomplished bydirecting heat to a targeted region, wherein the targeted region may bea flight surface's leading edge.

In certain aspect, heat may be directed to a targeted region by reducingthe resistance of a conductor, or portion thereof, positioned at thetargeted region.

In certain aspect, the resistance of the conductor may be reduced byincreasing the amount of conductive material at the targeted region.

In certain aspect, heat may be directed to a targeted region byconfiguring the orientation and geometry of the one or more conductorsrelative to the flow of electricity.

In certain aspect, the composite conductor assembly may comprise a firstand a second conductor, which are independently controlled such that theelectric power source selectively passes electric current through thefirst or the second conductor. In certain aspect, at least one of saidone or more conductors comprises a carbon nanotube material or a nickelchemical vapor deposition material.

In certain aspect, at least one of said one or more conductors ingressesor egresses the multi-functional composite system while maintainingelectrical isolation between the composite structure and the one or moreconductors.

In certain aspect, the composite conductor assembly, the plurality ofstructural composite fiber layers, and the matrix material aregalvanically or thermally similar.

In certain aspect, the composite conductor assembly further comprises ashielding material.

In certain aspect, at least one of said one or more insulating layerscomprises Poly Ether Ketone Ketone or etched, bondablepolytetrafluoroethylene.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages of the present invention will be readilyunderstood with reference to the following specifications and attacheddrawings wherein:

FIG. 1A illustrates an embedded CSA co-cured within a representativestructure;

FIG. 1B illustrates an embedded CSA co-bonded within a representativestructure;

FIG. 1C illustrates an embedded power and signal harness (e.g., CSA)co-bonded with a spar;

FIG. 2A illustrates an embedded CSA with printed circuit board connectorat ingress/egress points;

FIG. 2B illustrates a first length wise cross-sectional view of alaminate composite structure having an embedded CSA;

FIG. 2C illustrates a second length wise cross-sectional view of alaminate composite structure having an embedded CSA;

FIG. 3 depicts two graphs illustrating that embedded CNT signalperformance is consistent with copper performance for both serial and 10megabit Ethernet Systems;

FIG. 4 depicts a section of an example aircraft wing suitable ofembedded harness application;

FIG. 5 is a graph illustrating an example CNT embedded heater test paneltemperature rising overtime;

FIG. 6 is a graph illustrating an example NiCVD embedded heater testpanel temperature rising overtime;

FIGS. 7 a through 7 d illustrate an example wing leading edge withembedded electronics;

FIGS. 8 a and 8 b illustrate a graph of an example external surfacetemperature as a function of heat input;

FIG. 9 illustrates a chart of example ingress/egress layupconfigurations; and

FIG. 10 illustrates an example ply layup for CNT heater strips andsurrounding carbon structure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be describedhereinbelow with reference to the accompanying drawings. In thefollowing description, certain well-known functions or constructions arenot described in detail since they would obscure the invention inunnecessary detail. For this application the following terms anddefinitions shall apply:

The term “conductor sandwich assembly” (“CSA”) as used herein describesthe structure formed when one or more conductors (e.g., carbon, metal,NiCVD, etc.) are sandwiched between insulating layers of material suchthat the conductor is electrically isolated and structural loads (i.e.,shear, tension, compression, bending, and combined loads) can be passedtherethrough. As discussed herein, a CSA may be configured to carrypower and/or signals via the one or more conductor traces. A CSA mayfurther include one or more shielding layers to reduce, or eliminate,interference to any signal carrying conductors or by any power carryingconductors. A CSA may be embedded deep within a structure (e.g., acomposite structure) or embedded at, or adhered to, the surface of astructure.

The term “composite material” as used herein, refers to a materialcomprising an additive material and a matrix material. For example, acomposite material may comprise a fibrous additive material (e.g.,fiberglass, glass fiber (“GF”), carbon fiber (“CF”), aramid/para-aramidsynthetic fibers, FML, etc.) and a matrix material (e.g., epoxies,polyimides, aluminum, titanium, and alumina, including, withoutlimitation, plastic resin, polyester resin, polycarbonate resin, castingresin, polymer resin, thermoplastic, acrylic resin, chemical resin, anddry resin). Further, composite materials may comprise specific fibersembedded in the matrix material, while hybrid composite materials may beachieved via the addition of some complementary materials (e.g., two ormore fiber materials) to the basic fiber/epoxy matrix.

The term “composite laminates” as used herein, refers to a type ofcomposite material assembled from layers (i.e., a “ply”) of additivematerial and a matrix material. For example, layers of additivematerial, such as fibrous composite materials, may be joined to providedesired engineering properties, including inplane stiffness, bendingstiffness, strength, and coefficient of thermal expansion. Layers ofdifferent materials may be used, resulting in a hybrid laminate. Theindividual layers may be orthotropic (i.e., principal properties inorthogonal directions) or transversely isotropic (i.e., isotropicproperties in the transverse plane) with the laminate then exhibitinganisotropic (i.e., variable direction of principal properties),orthotropic, or quasi-isotropic properties. Quasi-isotropic laminatesexhibit isotropic (i.e., independent of direction) inplane response butare not restricted to isotropic out-of-plane (bending) response.Depending upon the stacking sequence of the individual layers, thelaminate may exhibit coupling between inplane and out-of-plane response.An example of bending-stretching coupling is the presence of curvaturedeveloping as a result of inplane loading.

The term “composite structure” as used herein, refers to structures, orcomponents, fabricated, at least in part, using a composite material,including, without limitation, composite laminates.

As discussed above, existing traditionally bound wire harnesses sufferfrom a number of drawbacks in that they can be, for example, heavy,voluminous, and subject to shorts, especially in connection with movablestructures. Further, traditionally bound wire harnesses are also limitedin that they cannot be used in certain locations due to size or weightconstraints. These problems and risks, however, are greatly reduced byimplementing embedded conductor technology (e.g., for power and/orsignals) in lieu of traditionally bound wire harnesses. Accordingly, anobject of the present disclosure to implement a lightweight,streamlined, embedded conductor harness technology to be used in lieuof, or in conjunction with, traditionally bound wire harnesses.

Indeed, embedded conductor technology, which may be used to carry powerand/or signals, offers a number of advantages over traditionalharnessing. First, embedded conductor technology increases aircraftinternal volume by reducing the space typically reserved, or required,for traditional harnessing. Thus, embedded conductor technology isparticularly useful where space is limited because it does not requirespace consuming wire bundles, conduit, tie downs, and other hardwareassociated with traditional harness runs.

Secondly, embedded conductor technology increases durability as theembedded conductors are less likely to be impacted (e.g., nicked,rubbed, damaged, etc.) in operation and/or during maintenance. That is,reliability and durability is improved because the conductors areretained and secured within the vehicle's structure, whereby thevehicle's structure functions to protect the conductors with minimalinfluence to the structure. In certain circumstances, the embeddedconductor technology may further strengthen, or increase the rigidityof, the structure.

Thirdly, embedded conductor technology can reduce weight by eliminatingthe need for conduits, attaching structure, and reinforcing weightneeded for standard methods of securing cabling. Conductive compositematerials also offer a weight benefit as compared to traditional metalsand are typically more compatible with standard composite materials andresin systems in terms of thermal compatibility and galvanic properties,while providing anti-corrosive properties. Moreover, further weightreduction can be realized if previously non-structural elements, such asinsulation, are turned into structural (load bearing) elements.Fourthly, embedded conductor technology can reduce cost by lowering partcount, improving assembly time, and reducing maintenance. The part countis reduced because traditional conduit, tie downs, and other suchhardware are no longer required throughout the aircraft. Moreover,component may be quickly connected via connectors at ingress/egresslocations.

Finally, wide-area power resulting from dispersing the conductors acrossa surface increases survivability and reliability of the vehicle when asingle point failure occurs. In other words, distributing the powerand/or signal conductors over a large area (“wide-area”) is more robustin terms of damage survivability because there need not be a singleconductor to cut and any damage would be limited to specific conductors,not an entire bundle (as can be the case with traditional wiringharnesses).

Similarly, wide-area power facilitates the use of a multitude ofcomponents and sensors throughout the vehicle, in addition to motors, byproviding power and signal capability where such functionality was notpreviously possible. Indeed, embedded conductor technology increases thepotential for the introduction of health monitoring and distributedsensing capabilities. For example, embedded conductor technology mayfacilitate functionalities such as structural health monitoring (e.g.,embedded sensors), shielding (e.g., electromagnetic interference (“EMI”)shielding), anti-icing, and de-icing. Indeed, monitoring and sensingcapabilities/infrastructure (e.g., sensors and associated wiring) may belaid up as part of the composite structure (e.g., embedded during themanufacturing, co-cured or co-bonded) fabricated process. Thus, embeddedconductor technology may be employed to provide resistance readings as adata feed input to certain systems.

Historically, health monitoring and distributed sensing capabilitieswere inadequate due to the limitations and bulk of traditional wireharnesses. The embedded conductor technology would be pertinent to othertechnologies. The use of embedded conductor technology facilitatesimproved sensor technology by eliminating the space constraintassociated with traditional harnesses. Thus, embedded sensortechnologies may be applied to a broad spectrum of applications invehicle control (such as Fly-By-Feel and other unmanned aerial vehicles(“UAV”) and systems), assessing mission performance, and cost benefits.

Embedded conductor technology can also provide a thermal conduction pathto reject unwanted heat through the structure, which would in turnreduce drag and weight as compared to traditional heat rejectionmethods. In fact, the vehicular structure may be designed to provide lowthermal resistance path for heat rejection. For example, when servos arejoined to, or embedded in, an aerial vehicle's wing's compositestructure, undesired heat through the structure may be rejected, asopposed to traditional methods that absorb the heat, thereby reducingdrag and weight.

Furthermore, as more composite aerial vehicles are developed, a greaterneed exists for a de-icing and/or anti-icing solution that does not relyon engine bleed air (e.g., warm/hot air from the engines). Epoxy andBis-Maleimide (“BMI”) pre-impregnated resin systems (“pre-preg”, i.e.,composite fibers having uncured matrix material already present) are thetwo more common composite matrices used in aircraft structures; however,neither of these is capable of withstanding the temperatures typicallyassociated with engine bleed air (typical values can be 200-250° C. and275 kPa (40 pounds per square inch (“PSI”)), forcing metal components tobe used where bleed air is used. As expected, such metal componentsincrease both cost and weight of the vehicle. However, as explainedbelow, conductive composite materials may function as embedded heatersto perform de-icing and/or anti-icing functions without requiring suchmetal components, while also keeping the temperature of the compositematerial within operational limits. Thus, embedded conductors may carryhigh power to the motors while simultaneously heating the surface of thevehicle (e.g., a leading edge of a wing) for de-icing and/or anti-icing.

In view of the above, an embodiment of the present application teachesan economical, lightweight conductor/wire harness and wire harnesssystem capable of being embedded within the structure and/or body panelof a vehicle. Such embedded conductor technology may be accomplished bysandwiching electrical conductors between two or more insulating layersof material such that the one or more electrically isolated conductorsform a CSA. The CSA may be embedded within the structure itself (e.g.,during the fabrication of a composite structure) or embedded on (oradhered to) the surface of a pre-fabricated structure. Once assembled,structural loads may then be passed through the CSA.

Such embedded conductor systems may be employed in areas wheretraditional wiring is prone to damage or where traditional wires cannotbe easily run. For example, aircraft wheel wells and wing trailing edgesare places where traditional wiring may be found hanging from structuresand can be damaged by moving parts such as gas struts. Other appropriateareas in which embedded conductor systems may be employed include areaswhereby cabling would typically be subject to damage or otherwiseimpractical, such as: rear spars adjacent to flaps, ailerons, andspoilers; long runs of cabling with several connection nodes such alongwing (spars, stringers) or fuselage (longerons, keels) structures;electrical systems which required distributed networks of wiring such asfor structural health monitoring, temperature monitoring; compartmentheaters such as for avionics or wall/floor heating of passengercompartments; ice protection systems such as de-icing and/or anti-icingsystems; lightweight heater pads such as hot plates; and automobileheating systems. In addition, the embedded conductor systems furtherfacilitate all electric aircraft, thereby doing away with hydraulicactuators and replacing them with electro-mechanical actuators.

A CSA may further comprise one or more shielding layers to reduce, oreliminate, interference to any signal carrying conductors. The shieldinglayers may also act to reduce any interference created by power carryingconductors. Thus, in addition to carrying power and/or data signals,embedded conductors within a composite laminate structure may provideEMI shielding and resistive heating functionalities. EMI shielding maybe provided, for example, to shield components from externalfrequencies. To that end, dielectric materials may be incorporatedwithin a traditional composite laminate structure to provide aconductive barrier between the structural materials and conductivematerials (e.g., those conductive for power/signal transmission). Forexample, tests illustrated that test coupons with three sheets (i.e.,three plys) of CNT improved shielding from the baseline coupons byapproximately 10 dbm, whereby a wingtip EMI article illustrated 10 dbmattenuation from the baseline.

Indeed, embedded conductors and insulating layer materials may becompatible with existing structures (e.g., a composite structure) toprovide a specific functionality. For electrical purposes, power andsignal cabling, EMI shielding, resistive heating, capacitance andimpedance matched conductors can be embedded within laminate. Theaddition of this capability provides additional structural benefits suchas structural strength, stiffness, resistance to moisture ingress,impact resistance, and durability depending on the materials selectedand layup configuration of components. For example, mechanical impacttests on panels showed that CNT sheets improve damage tolerance over thebaseline to varying levels depending on the location within the layup.

As disclosed herein, a CSA, with or without shielding layers, may beincorporated into and/or onto a composite structure without negativelyimpacting the electrical and structural properties of the incorporatedsystem. In such situations, the conductive and dielectric materials mayfurther provide structural functionality to the composite structure. Tofacilitate interconnection with other components or systems, embeddedconnectors (e.g., an electrical connector) may be provided at thesurface of the composite structure to interface with traditionalpower/signal transmission devices. Thus, the embedded connectors, whichare electronically coupled to the embedded conductor(s), may beconfigured to ingress/egress in/out of the composite structure'scomposite material plys while maintaining isolation between the embeddedconnectors and composite structure. Indeed, using embedded conductortechnology, multi-functional vehicle sections/components (e.g.,multi-functional wings, such as those illustrated in FIGS. 7 a-7 c) maybe provided that incorporates both embedded data processing andstructurally embedded power systems.

Embeddable Conductors. A number of materials may be used as the suitableembedded conductors. Such materials may include, for example, carbonbased conductors (e.g., CNT material, CNF material, NiCVD carbonnonwoven materials), metallic conductors (e.g., copper, gold, silver,metal deposited polyester nonwoven material), other materials (e.g.,Nickel/Copper Polyester Nonwoven), or a combination thereof. CNTmaterials and NiCVD material are generally discussed herein as thepreferred conductors; however alternative conductors, including metallicconductors, may be similarly used and are contemplated. In certainaspects, when metallic conductors are employed, aluminum would be apreferable metallic conductor.

Over the last decade, CNT material has become an increasingly viablematerial for structural and electrical uses. Generally, CNTs areallotropes of carbon with a cylindrical nanostructure and are an idealconductor for an embedded signal application. Another possible conductormay be CNF. CNFs (a.k.a vapor grown carbon fibers (“VGCF”s) or vaporgrown carbon nanofibers (“VGCNF”s)) are nanostructures with graphenelayers arranged as stacked cones, cups, or plates, whereas CNTs arecarbon nanofibers with graphene layers wrapped into cylinders. Generallyspeaking, CNTs and CNFs are superior to copper in terms of embeddedconductor and harness application. First of all, copper has a highercoefficient of thermal expansion (“CTE”) than carbon (copper is˜16.6×10-6 m/m K, while carbon is ˜2×10-6 m/mK), which causes a changein volume in response to a change in temperature, lower strength, and ahigher modulus which inhibits its flexibility. Secondly, copper is alsoprone to strain hardening, which weakens the copper material over time.These factors combine to make copper highly susceptible to breakage anddamage as an embedded harness. However, CNFs' and CNTs' CTE, lowmodulus, and high strength have the exact opposite effect, combining tohandle large temperature swings and vibration, while deflecting with thestructure. For these reasons, CNT and CNF materials are superior tocopper for harness and wiring embedment. In addition, CNTs and CNFs canbe folded and bent onto themselves without breakage, allowing them to berouted in the sharp corners and curves of composite structures. Thisproperty and their high strength enables CNF and CNT embedded harnessesto have tight bend radii when exiting connectors. For example, moderncarbon conductor materials, such as Nanocomp's conductive CNT yarn andsheet media, exhibit a high strength, high conductivity, and low moduluscompared to other traditional carbon materials. These features make themattractive for embedded harnessing applications. It is also estimatedthat there will be a cost and weight reduction by using embedded CNTs asthe CNT material expectedly improves. In order to realize thesereductions, development of conductor embedment that is structurally andelectrically stable, while being lightweight, is essential.

In testing the usability of CNT conductor materials within a compositestructure's resin layup, measurements were taken using 0.5- by 8-inchlength strips (“coupons”) of Nanocomp 15 gsm CNT sheet materialimpregnated with Patz Materials and Technology's PMT-F4 resin (a highlytoughened epoxy resin system designed for vacuum bag, press andautoclave curing using standard layup procedures). The PMT-F4 resin canbe impregnated into numerous reinforcements and imparts a medium/drytack and compatible with standard 250° F. release materials and baggingprocedures.

The resistance along the 8-inch length strips was measured using anExtech Instruments precision milliohm meter before layup and after layupcure to identify any variations within the CNT conductors. Theresistance of each CNT conductor coupon was measured in the curedcondition using several different conductive epoxies at the connectorsites. The data calculated indicates that the resistance after curing isapproximately double that of the resistance prior to curing, but theresistance variation between coupons was nominal, despite the epoxyselection.

While CNT results were promising, NiCVD materials were similarlyinvestigated as an alternate conductor material. From a conductivitystandpoint, the NiCVD is better as a power conductor due to higherspecific conductivity (i.e., 866 S-cm²/gm, versus CNT's 238 S-cm²/gm).As with the CNT testing, the resistance along the 8-inch length of NiCVDmaterial was measured using an Extech Instruments precision milliohmmeter prior to layup and after layup cure to identify any variationswithin the NiCVD conductors. Again, the resistance of each NiCVDconductor coupon was measured in the cured condition using severaldifferent conductive epoxies at the connector sites. The NiCVD conductorcoupon measured low resistance with no significant change after 250° F.cure.

In view of the tests, an advantage of the NiCVD material is the lowresistance. Moreover, NiCVD material may be a suitable replacement forCNT material as an embedded conductor because of lower cost. NiCVDmaterial is currently approximately 10-20 percent of the cost ofcomparable CNT material, depending on the electrical application. Oneply of film adhesive (i.e., 3M AF163) was also found to work well withthe nonwoven material and did not increase resistance. Basic electricalproperty relationships were determined for the CNT and NiCVD sheetconductor materials, whereby it was determined that NiCVD Nonwovenexhibited greatly reduced resistivity and resistance post-cure vis-à-visCNT, while illustrating incread average conductivity and averagespecific conductivity. More specifically, the resistance of CNT wasfound to be about 4-7 times higher than NiCVD Nonwoven, while theconductivity of the NiCVD Nonwoven was found to be about 3.6 to 4.5higher than CNT. However, in certain situations, CNT and NiCVD and beemployed together to achieved a particular goal based on a desiredresistance and conductivity.

To investigate the usability of NiCVD material as an embeddableconductor (e.g., in a CSA), an article was fabricated using NiCVD coatednonwoven sheet, 20 gsm and 45 gsm, and NiCVD coated zylon (i.e.,poly(p-phenylene-2,6-benzobisoxazole)) in place of CNT sheet and yarnmaterial. Yarn conductors provide a higher volumetric efficiency,however it can be more difficult to incorporate into a CSA withoutdetrimental effect on the structure.

Further, a FML may also be used to facilitate multi-functionalstructures because an FML already includes both a conductor (i.e., metalbayer) and insulators (i.e., composite material layer). That is, FMLtypically comprises a laminate of several thin metal layers bonded withlayers of composite material. For instance, a plurality of thin layersmay be spaced between one insulating sheet, such as GF. The entirestructure may share the same resin/epoxy matrix. Accordingly, the sameelectrical functionality discussed above with regard to CNT and NiCVDmaterials may be achieved using FML, The metal conductor material may becut separately and laid up into the laminate as well. Alternatively,conductive sheet materials (CNT, Nickel Nonwovens, etc.) can be added toFML if the resistance of the parent material is not appropriate for theapplication. As illustrated in FIG. 7 d, a gap may be created within ametallic layer between metal structures to form a circuit. This gap isfilled by the insulating layer (e.g., GF) and epoxy/resin matrix.

Layup. An embedded conductor harness layup schedule may comprise acombination of composite materials with conductor materials forconducting electricity (e.g., CNT yarns, CNT sheets, Nickel Non-Wovens,Non-Woven Carbon Fiber Veil, copper, aluminum mesh, etc.) therebetweenand dielectric materials, which may also act as structural reinforcing(such as GF) or may not act as structural materials (e.g., PEKK polymer,Kapton). As disclosed herein, the embedding process itself is notconductor material specific, but instead may be adapted as CNT material,NiCVD material, and as other materials are matured or developed. Theharness layup typically involves creating a harness within thestructural laminate or on top of The harness conductors may be layeredin a fashion similar to a printed circuit board (“PCB”), wherein theconductor materials utilize a compatible resin system and aregalvanically and thermally matched to the structural composite material.

For example, a harness layup may further employ tailored dielectricmaterials such as PEKK laminates or glass laminates with specific resinweight contents and/or resins with higher dielectric strengths.Similarly, a harness layup may tailor the separation of conductivelayers via the dielectric layers to achieve specific electricalproperties (e.g., impedance matching, capacitance, etc.). Further, tomitigate the risk of shorts resulting for water permeation, additionallayers may be provided over the conductor(s) to act as a moisturebarrier. For example, testing revealed that three suitable moisturebarriers include, without limitation: (1) Single 120 glass fiber plywith additional resin; (2) Single glass fiber MTM45-1 GF0103 ply; and(3) Surfacing film/Single 120 glass fiber ply.

Power System Embedment. An embedded power harness (e.g., a CSA enabledfor carrying power) may be made of the one or more layers ofnon-impregnated conductor sheets (e.g., CNT, NiCVD, etc.), sandwiched(e.g., inserted between) between two or more layers of insulating film(e.g., fiberglass, typically 5 mil) and a film adhesive (e.g., aircraftfilm adhesive) with moisture barrier (e.g., FM300-2 MB, a moisturebarrier film adhesive). The moisture barrier material may be, forexample, a FM300-2 Moisture Barrier product available from Cytec, orlaid up using a layer of PEKK (e.g., around 0.0014 inch thick) andadhesive resin film. Fiberglass layers provide insulation and stabilitywhile the film adhesive provides a moisture barrier and a bond to thesurrounding carbon composite. The fiberglass can also provide up to2400V of breakdown resistance (an attribute that is critical for theembedded system because power systems can often carry high voltages, andany breakage or fracture in the insulating film could lead to ahazardous short circuit). In certain embodiments, the insulating filmmay comprise an etched, bondable polytetrafluoroethylene (“PTFE”) (e.g.,Teflon, available from DuPont). For example, PTFE material may be etchedwith sodium ammonia or sodium naphthalene so as to chemically modify thesurface for adhesion to various substrates using ordinarycommercial-grade epoxies. When etched for bonding, PTFE may be glued tosurfaces to produce a non-stick, low-coefficient-of-friction unit.

As discussed in greater detail below, a CSA may be laid up (e.g.,co-bonded or co-cured) with a composite material or structure and, oncecured, becomes part of the composite structure (e.g., a spar, wing,etc.). During embedment, the CSA (or even individual conductors) may beimpregnated as part of the layup (e.g., impregnated during manufacturingof the composite structure, co-cured). Because the CSA is protected bythe structure material, there is less opportunity for damage duringoperation and maintenance. In certain embodiments, depending on thethreat of liquid for a particular application, one or more additionalbarriers may be added to protect against liquid intrusion. Thesebarriers may be incorporated within the CSA or around the CSA duringcuring/embedment. In certain embodiments, the liquid epoxy used tofabricate the composite structure may also be used to bond the one ormore carbon conductors and the one or more layers to form the CSA. Incertain embodiments, such as when co-cured, one or more conductors maybe placed directly in the composite material of the structure prior tocuring such that they do not make unwanted contact with anotherconductor. This arrangement eliminates the need for insulating layers asthe non-conductive composite material of the structure would isolate theconductors and prevent unwanted contact with other conductors.

Signal System Embedment. Signal harnesses (e.g., a CSA enabled forcarrying data signals, whether analog or digital) require higher levelsof quality and complexity as compared to electrical power systems. Forexample, to prevent inaccurate or weak signals, most conductive signalsystems require strict voltage control while utilizing very smallcurrents, where it may be common to drive mega-ohm loads. For embeddedsignal conductors, individual conductors (e.g., CNT yarn or NiCVD yarn),shields (e.g., EMT shields), a fiberglass insulator and a moisturebarrier may be used to form the CSA. With the assistance of an adhesiveor resin, the CSA may then be applied as a laminate tape. This signalharness may also be laid up with the embedment material andingresses/egresses similar to the power system embedment. Signalembedment benefits from the same protection as power system embedmentwhile also gaining from the significant weight savings that CNTs offerfor signal conductors and shields.

Power and Signal System Embedment Testing. To verify the usability ofthe embedded power/signal harnesses, applicant Aurora Flight Sciencesfabricated an aircraft spar based upon Aurora's Orion aircraft havingembedded power and signal harnesses. The harness was co-bonded onto anaircraft spar cured on a male aluminum tool with 8 plys of carbon fibermaterial in the cap (i.e., the edge) and 4 full plys over two sectionsof a core material, which were cured with film adhesive on each side.Peel ply was applied to the tool side to provide a surface for bondingthe harness in a second cure.

Three separate 6 foot harnesses were fabricated on the spar web andco-bonded through a 250° F. cure, including a high amperage harness, alower amperage harness, and a signal harness. The high amperage harness,which was shielded, was fabricated using copper mesh boarded to acentral harness, which contained the low power harness and the signalharness. The various conductors were configured to interface with PCBconnectors at each end of the aircraft spar. Shielding was providedusing Nanocomp 15 gsm, acid etched CNT sheets impregnated with PatzPMTF-4 resin film and constructed as two individual plys, whichsandwiched the power and signal conductors. The low power conductorswere fabricated from three plys of impregnated 40 gsm, 0.375-inch wideNiCVD strips from Conductive Composites. The signal wires were providedvia 10 and 12 HighTex CNT yarns (two of each). 120 fiberglass pre-pregwas used as insulating layers between the low power conductors and theshielding. The 120 fiberglass pre-preg was also used to isolate theentire harness from the carbon of the spar. Although preliminary testsillustrated that two plys of glass could provide sufficient isolationand conductively insulate the harness up to 1,000V, this appeared to behighly affected by the resin content and final porosity of the curedglass plys. Accordingly, three plys of glass were used as the baseisolation between the harnesses and the spar to ensure adequateinsulation. The conductors (i.e., traces) were fabricated in two plysets. During the first set, low power trace 1, and signal traces 3 and 5were laid up. After two plys of glass, the second ply set of low powertrace 2 and signal traces 4 and 6 were laid up. This was done to providea better isolation between adjacent traces and to reduce the chance ofshorting between them. Glass plys were dropped approximately 0.25-inchfrom the end of each trace allowing a pad of the conductive material tobe exposed to the bag side during cure which would later act as theinterface to the PCB.

More specifically, the embedded test power/data signal harness layup wasassembled as follows: film adhesive; 3 plys 90 degree 120 GF; CNT shieldply; 2 plys 90 degree 120 GF; 3 plys NiCVD (low power trace 1); 12strand CNT yarn (signal 3); 10 strand CTN yarn (signal 5); 2 plys 90degree 120 GF; 3 plys NiCVD (outer power trace); 12 strand CNT yarn(outer signal); 10 strand CNT yarn (inner mid signal); 2 plys 90 degree120 GF; 2 plys NiCVD (inner power trace); 12 strand CNT yarn (outer midsignal); 10 strand CNT yarn (inner signal); 2 plys 90 degree 120 GF; CNTshield ply; and 2 plys 90 degree 7781 GF. Concurrently the large powerharnesses were assembled on either side of the central harness. Theembedded power harness layup for the copper power harnesses was asfollows: film adhesive; 3 plys 90 degree 7781 GF; Copper mesh withattached leads; and 2 plys 90 degree 7781 GF. Additionally small NiCVDpads were added to the end of each CNT yarn to allow more area forconnection to the PCB connectors. These pads were approximately 0.13- by0.25-inch long.

The embedded power harness was subjected to two power transfer tests;one with 120 VAC at 20A for a total of 2400W transmitted and anotherwith 28 VDC at 50A for a total of 1400W transmitted. The temperaturerise in each test was 10° F. and 40° F. respectively. At 50A of current,the 6 foot system was acceptably efficient and dissipated 160W of powerin the harness. As will be discussed below, this temperature increasemay be used, or further manipulated, to facilitate de-icing and/oranti-icing functions.

The embedded central harness was subjected to testing of both the lowpower harness and signal harness. The low power harness was tested using28 VDC at 0.5 A. The conductive NiCVD pathways did not display any hotspots or any significant heating above ambient temperatures (˜5° F.).Non-detrimental heating (an increase of approximately 20° F.) at theconnection site between the PCB and the embedded harness was detected,thus the Z-axis connectors used may be modified in future applicationsas a solid connection across the entirety of the area of the connectionpad site. The low power harness was also tested at 0.75A and 28VDC wherethe temperature on the NiCVD pathways increased slightly (an increase ofapproximately 5° F.). The signal harness was tested with a 12.5 MHZ 50percent duty cycle square wave with a 5 Vpp amplitude and a 25 MHZ, 5Vpp sinusoid. In both cases the significant inline resistance led to anacceptably signal voltage division loss, but even with this loss thesystems were still well within standard transfer ranges for 10BTEthernet, CANBUS, and RS-485 Serial. There was no evidence of thenon-linearity or being out of symmetry in signals. Thus, the testingindicated that the test harnesses were, in terms of performance, asuitable replacement for traditionally bound wires.

Ingress/egress. Ingress/egress of embedded harnesses requires particularcare in order to protect both the embedded harness (e.g., theconductors) and the embedment composite material. Generally,ingress/egress points are a stress and wear point for damage to theharness and present a potential point for water, fuel, and foreigndebris to enter the embedment composite material. To counter thisproblem, various methods have been devised utilizing materials such asstranded insulated wire, flex PCBs or methods that employ compliantinterfaces to transfer power in the Z-axis (thru plane) only to PCBs,connection pads, or other traditional interfaces/connectors. Further,the materials (e.g., the conductors), may be stepped through structurallayers or plys of the composite structure, while maintaining isolationbetween structural materials and conductive material. In other words,rather than vertically penetrating the various layers at a single pointto egress/ingress the composite structure, thereby enablingmoisture/debris to penetrate straight to the core, the conductor(s) mayingress/egress in a gradual (e.g., one layer at a time), laterallyoffset manner such that moisture/debris penetration is inhibited.

For example, for power systems, the conductor may exit the embedmentcomposite material and lay on a nonconductive block. A threaded stud maybe installed (e.g., wet-installed) into the conductor layup and acts asthe mounting point for local harnessing. For signal harnesses, theconductor tape may exit the embedment material and be mounted to a PCB.This is a similar process to mounting inter-board ribbon connections andmay be, for example, soldered or compressed to the PCB. At this point,any number of connectors can be used to interface to the embedded signalharness. Because the harness is covered by the structure, there is lessopportunity for damage during operation and maintenance.

While certain of the Figures are generally described in the context ofCNT conductors embedded in an aircraft, the teachings and principles ofthe present invention may be applied to other conductive materials andvehicles without departing from the spirit and scope of the invention.For example, other conductive materials include, without limitation,NiCVD materials, metallic materials, and other embeddable conductorsknown to those skilled in the art, while other vehicles include, withoutlimitation, land craft and water craft. Therefore, the teachings hereinshould not be viewed as vehicle- or conductor-specific, but rather, maybe similarly applied to embedment of other materials in variousvehicles. For example, an ingress/egress approach was examined using 20gsm NiCVD coated nonwoven carbon veil in place of conductive epoxy atingress/egress locations on the CNT sheets. Resistance measurementsindicated that the connection performs very well. Thus, the nonwovenmaterial may be laid up with the CNT sheets during the impregnationprocess—a process that is generally easier to employ than conductiveepoxy.

FIGS. 1A and 1B illustrate an embedded harness 106 (e.g., a CSAcomprising one or more power and/or signal conductors) enabled for usein an aircraft (e.g., a UAV) flight control device (e.g., a servo—adevice used to provide control of a desired operation through the use offeedback). A typical aircraft flight control system comprises multiplecomponents, including, for example, flight control surfaces, therespective cockpit controls, connecting linkages, aircraft enginecontrols and the necessary operating mechanisms to control an aircraft'sdirection in flight. An embedded power and/or signal harness 106 can beused to electronically connect the various devices within a flightcontrol system. In fact, an embedded harness 106 may be used in place ofvirtually any wire currently used in an aircraft that travels along aservice which permits embedment or attachment.

The harness 106 may be embedded to the surface of a composite aircraftmember, for example, embedded inside, or embedded on the surface of, thecomposite aircraft member. In certain embodiments, the harness 106 mayembedded on the surface of a metal structure, provided the harness 106can be adhered to the metal and that insulation has been placed betweenthe conductors and/or any metallic structures such that they areelectrically isolated.

As illustrated in FIGS. 1A and 1B, a harness 106 may be embedded (e.g.,surface embedment, or deep (sub-surface) embedment within a compositestructure) in the spar 104 (e.g., an aft spar) of, for example, anaircraft wing structure. In either surface embedment or deep embedment,the harness 106 may be either co-cured 100 (FIG. 1A, wherein the CSA isinstalled in the composite structure as the composite structure is builtup and they are cured together) or co-bonded 102 (FIG. 1B, the CSA isbonded to a pre-fabricated structure, e.g., with a resin or otheradhesive) with the composite structure. The harness 106 may be embeddedalong the neutral axis on the composite structure to minimize loads andreduce the effects of flexing. If the composite structure is rigid, orflexing is not a concern, the harness 106 may be installed at any pointon the composite structure.

For embedment deep within composite structures (FIG. 1A), harness 106may be impregnated and co-cured 100 within the composite structure toprovide integrity with the surrounding structure and not act as astructural defect. The CSA should readily bond to the surroundingmaterials without creating voids or structural deficiencies. Forembedment close to, or at, the surface of the composite structure (FIG.1B), the harness 106 may not need to be impregnated within the compositestructure but only within the layers of protective material surroundingconductors, which may be co-bonded 102 to the composite structure in asecondary operation (e.g., with a resin or adhesive). The ability toco-bond a harness 106 to a structure in a secondary operation may enableretro-fitting of existing vehicles and aircraft with embedded conductortechnology. This would be particularly useful in instances whereadditional sensors may be desirable but were previously difficult toexecute due to traditional wiring techniques. For example, amulti-conductor CSA harness may be manufactured as a combination ofconductors, insulating film layers, and film adhesive and delivered in aform ready to be installed into a composite layup, and co-cured withsaid layup. Similarly, the multi-conductor CSA may also be enabled forinstallation on a traditional metallic structure, provided themulti-conductor CSA is insulated such that no electrical contact existsbetween the conductors and the metallic surface.

Although they are equally electrically conductive, co-cured 100 andco-bonded 102 configurations each have certain advantages. For example,co-cured 100 embedment is typically more durable because the harness 106is deep within the composite structure material and thus the CNT isprotected by the composite structure material; however, co-bonded 102embedment is superior with respect to ingress/egress because the CNTharness is embedded at the surface and not deep within the compositestructure, therefore providing easy access to surface connectionswithout potentially weakening the composite structure's integrity.Similarly, co-bonded 102 embedment is more easily manufactured becausethe harness 106 may be simply applied to a surface of a structure in asecondary operation and does not require the simultaneous fabrication ofthe composite structure and the embedded harness 106. However, co-cured100 embedment eliminates excess weight because it does not requireadditional protective/insulation layers or adhesives that are typicallyused to adhere and protect co-bonded 102 harnesses 106. In view of theabove benefits attributed to each embedment type, a designer ought toweigh the factors and determine which would be more applicable to his orher particular project. For example, an aircraft developed for UAV usemay require additional durability while eliminating weight and maytherefore prefer co-cured 100 embedment. Regardless of the embedmenttype, the harness 106 may run along the length of the spar 104 (or othercomponent) until reaching, for example, the flight control servolocation where the harness 106 would egress to provide the necessarypower and signal input to the servo.

FIG. 1C illustrates an embedment of an example CSA having both power andsignal conductors in a long endurance aircraft wing spar 104 using CNTconductors 106. As seen in the Figure, power conductor 106A and signalconductor 106B CSAs are co-bonded 102 to the surface of spar 104 in theform of a laminate tape 114 (or beneath such a tape) and haveingress/egress connection points for both the power connections 110 andthe signal connections 112. A number of connector types are possible,including, for example, 8P8C connectors (a.k.a eight positions, eightconductors), D-subminiature connectors, USB connectors, serialconnectors, parallel connectors, power connectors, radio frequencyconnectors, DC connectors, registered jack connectors (e.g., RJ-XX),etc. To prevent electrical failures and/or malfunctions, regardless ofthe connection type used, the connector should also be non-corrosive andnot paired with another material that may lead to corrosion. Forexample, a problem discovered by a Kelly AFB engineer trained incorrosion control was the corrosion of tin-plated electrical connectorpins when mated with gold-plated sockets used in the F-16 fighter. Atpoint A, FIG. 1C depicts examples where CNT conductors have been foldedand bent onto themselves without breakage, allowing them to be routedinto the sharp corners and curves of both composite and non-compositestructures. This feature of CNT conductors makes them an ideal conductorfor small spaces with sharp bends and turns.

FIG. 2A illustrates a composite structure 212 with an embedded CSA 216having both sheet-shaped power 204 and yarn signal 206 conductorscoupled with a PCB 202 for ingress/egress of the composite structure212. As seen in the figures, the CSA 216 may be fabricated from multiplelayers of CNT sheet 204 and yarn 206 sandwiched between layers of apolymer insulator 208 (e.g., fiberglass pre-preg, bondable polymer film,and/or moisture barrier film adhesive) to form a CSA enabled to carryboth power and electrical signals. Fiberglass pre-preg is readilyavailable but, as a woven material, may allow a conductor fiber topenetrate through the weave to cause shorting or power loss. Thus, analternative polymer insulator may further include moisture barrier filmadhesive, such as a material originally intended to keep moisture frombeing absorbed into a honeycomb core. Moisture barrier film adhesive maybe made from a thin layer of PEKK (Poly Ether Ketone Ketone), called aninterleaf, and film adhesive and/or matrix resin on the sides of thePEKK. For example, a suitable off-the-shelf moisture barrier product isFM300-2 Moisture Barrier, available from Cytec. Alternatively, amoisture barrier may be hand laid up using 0.0014-inch thick PEKK andfilm adhesive. As seen in FIG. 2A, shield layers 214A, 214B areinstalled within the CSA 210 on each side of the CNT conductors toshield any noise (e.g., electromagnetic compatibility (“EMC”) and EMI).In signal applications, such interference must be reduced as it may leadto weak and/or inaccurate signals. The CSA 210 (including any CNT sheetmaterials 204, 206) may be impregnated prior to the start of assembly(co-cured) or may be placed into the layup using the same process forfabricating a carbon epoxy layup (co-bonded).

In addition, a conductive epoxy may be used to prevent resin flow intothe CNT during impregnation while also providing for an attachmentmethod to a PCB 202. While this method allows for connection, theprocess may not be ideal for a manufacturing environment and can addweight that may be avoided using alternate methods. An alternativeingress/egress approach may be to use 20 gsm NiCVD coated nonwovencarbon veil in place of conductive epoxy at ingress-egress sites on theCNT sheets. Resistance tests show that the connection performs verywell. The NiCVD material may be laid up with the CNT sheets during theimpregnation process. Another solution would to electroplate the ends onthe CNT sheet 204 and/or yarn 206 with a metal (e.g., tin, gold, copper,etc.). This electroplating process allows for a reduced system weight incomparison to conductive epoxy and reduces the overall stack-up height(e.g., thickness) of the PCB 202 connection. Electroplating the ends ofthe conductors with a metal also allows for easier connection to asecond conductor outside the composite structure 212. The materials forattachment of the tinned CNTs to the PCB 202 or other connector 210should be manufactured to military specifications and/or using militarymaterials and processes. Furthermore, methods for plating of CNT's endsprevents resin flow into the area and allow for easy attachment to PCBsor other connectors using traditional materials.

FIG. 2B illustrates a first length wise cross-sectional view of alaminate composite structure 212 having an embedded CSA 216. Asillustrated, the laminate composite structure 212 may generally comprisea core 218, and a plurality of structural layers 220 (e.g., compositematerial layers 220 a, 220 b, 220 c, 220 d, 220 e). The structurallayers 220 may be, for example, a dry composite material, carbonpre-preg, or any other suitable composite material ply. While fivestructural layers 220 are illustrated, one of skill in the art wouldappreciate that additional, or fewer, layers 220 may be employed asdesired for a particular application. Thus, the use of five layers 220is merely illustrative and the present teachings should not be construedas limited to layups having five layers.

More specifically, FIG. 2B illustrates a technique for stepping the CSA216 through structural layers 220, or plys, of the composite structure212, while maintaining isolation between structural materials (e.g., thestructural layers 220) and conductive material (e.g., the CSA 216 orconductors within). As discussed above, merely penetrating the variouslayers 220 at a single point enables moisture/debris to more easilypenetrate to the core 218 of the composite structure 212, thuspotentially weakening the structural integrity of the compositestructure 212. However, embedding the CSA 216 in a gradual, laterallyoffset manner (e.g., shifting and stepping one structural layer 220 at atime) to ingress/egress through a stepping process prohibits, ormitigates, the risk of moisture/debris damage.

Throughout the stepping processes of FIGS. 2B and 2C, the CSA 216 may beconfigured to traverse (e.g., penetrate a layer, or “step”) from onestructural layer 220 to another layer 220 at a slight angle (e.g., 15 to45 degrees) or vertically (i.e., 90 degrees, or perpendicular to thecore 218). However, transitioning at a slight angle, as illustrated, canmitigate any strain associated with forming a 90 degree bend in the CSA216.

Further, as illustrated, to maintain a substantially even thicknessacross a laminate composite structure 212, the CSA 216 may beapproximately the same thickness as a structural layer 220 (or group oflayers) such that the CSA 216 can effectively fill the void of a removedstructural layer 220, or portion thereof. That is, a structural layer220 may be effectively removed and substituted with the CSA 216 at agiven depth.

Ingress Stepping. As illustrated, a first connector 210 may bepositioned at point A. The CSA 216 (which may be operatively coupled tothe first connector 210 as discussed with regard to FIG. 2A) may beconfigured to ingress the composite structure 212 at point A, therebyinwardly traversing from the surface of the laminate composite structure212 such that a first portion of the CSA 216 resides between fifth layer220 e and third layer 220 c (i.e., occupying a void of a removed/omittedcorresponding portion of the fourth layer 220 d). The first portion ofthe portion of the CSA 216 may then travel along a predetermine length(or distance) of the laminate composite structure 212 such that the CSA216 portion is substantially parallel to the layers 220 (and the core218).

The CSA 216 may then inwardly traverse another layer so as such that asecond portion of the CSA 216 resides between fourth layer 220 d andsecond layer 220 b. The CSA 216 may again travel along a predeterminelength of the laminate composite structure 212 such that the secondportion of the CSA 216 is substantially parallel to the layers 220. TheCSA 216 may then inwardly traverse another layer so as such that a thirdportion of the CSA 216 resides between third layer 220 c and first layer220 a. The CSA 216 may again travel along a predetermine length of thelaminate composite structure 212 such that the third portion of the CSA216 is substantially parallel to the layers 220. The CSA 216 may theninwardly traverse another layer so as such that a fourth portion of theCSA 216 resides between second layer 220 c and core 218. In the presentexample, the fourth portion would be considered the deepest point ofembedment.

Deepest Point. Generally, a majority of the CSA 216's length may beembedded at the deepest point so as to maximize CSA 216 protection(e.g., from damage). Thus, the CSA 216 may again travel along apredetermine length of the laminate composite structure 212 such thatthe fourth portion of the CSA 216 is substantially parallel to thelayers 220. Essentially, the CSA 216 may travel at the deepest pointuntil the CSA 216 approaches an egress location (point B), at whichpoint the ingress stepping process is repeated, but in reverse order, toegress.

While only a single span (e.g., the fourth portion) between layertraverse points is illustrated as being at the deepest point, it iscontemplated that the CSA 216 may reach the deepest point, and thenoutwardly traverses a layer so as to avoid an obstacle, only to inwardlytraverse a layer to return to the deepest point. Thus, two or morediscontinuations spans between layer traverse points may be positionedat the deepest point between the ingress/egress point A and B.

Egress Stepping. As illustrated, the CSA 216 may outwardly traverse alayer from the deepest point so as such that a fifth portion of the CSA216 resides between third layer 220 c and first layer 220 a. The CSA 216may again travel along a predetermine length of the laminate compositestructure 212 such that the fifth portion of the CSA 216 issubstantially parallel to the layers 220. The CSA 216 may then outwardlytraverse another layer so as such that a sixth portion of the CSA 216resides between fourth layer 220 d and second layer 220 b. The CSA 216may again travel along a predetermine length of the laminate compositestructure 212 such that the sixth portion of the CSA 216 issubstantially parallel to the layers 220. The CSA 216 may then outwardlytraverse another layer so as such that a seventh portion of the CSA 216resides between fifth layer 220 e and third layer 220 c. The CSA 216 mayagain travel along a predetermine length of the laminate compositestructure 212 such that the seventh portion of the CSA 216 issubstantially parallel to the layers 220. The CSA 216 may then traverseanother layer so as to egress at point B, where a second connector 210may be positioned. The CSA 216, which may be operatively coupled to thesecond connector 210 as discussed with regard to FIG. 2A.

FIG. 2C illustrates a second length wise cross-sectional view of alaminate composite structure 212 having an embedded CSA 216. Asillustrated at point C, depending on the need and type of compositestructure, the CSA 216 may traverse two or more layers 220 at a time(e.g., vertically or at a slight angle). For instance, if a large numberof layers 220 are used in manufacturing the composite structure 212,traversing the various layers one layer 220 at a time may beimpractical. Further, while FIG. 2B illustrates the CSA 216 as travelingadjacent (and substantially parallel) to the core 218, the CSA 216'sdeepest point need not always be embedded between the core 216 and thefirst layer 220 a. Rather, the CSA 216's deepest point may be configuredbetween any two desired layers, thereby enabling shallow or deepembedment. For example, as illustrated in FIG. 2C at point D, the CSA216's deepest point may be embedded between the first layer 220 a andthe second layer 220 b. Thus, one of skill in the art would appreciatethat various embedment arrangements are contemplated herein. Finally,while the connector 210 may be provided at the distal ends of the CSA216, it is contemplated that a connector may be provided at any portionbetween the distal ends of the CSA 216. For example, as illustrated inFIG. 2C, a portion may egress and ingress at point E such that aconnector 210 may be provided to transmit (e.g., tap) power or datasignals to or from CSA 216. As illustrated, the CSA 216 may egress atpoint E and travel along a predetermine length of the laminate compositestructure 212 such that the a portion of the CSA 216 is substantiallyparallel to the layers 220 before traversing one or more layers so as toegress at point F, where a third connector 210 may be positioned. Thismay be advantage where accessible power or surface mounted sensors needbe distributed along a surface without running a dedicated CSA 216.

To determine the mechanical capability of the embedded system of FIGS. 1and 2A-2C, an article containing embedded CNT conductors (via, forexample, a CSA 216) was tested by applying tensile and compressivestrains similar to those expected during pull up of a large scaleaircraft (e.g., UAV). The tests concluded that not only could thearticle withstand the strains when located near the neutral axis, butalso could sustain the bending strains of the spar caps withoutincreasing electrical resistance, a critical element to most electricalsystems. This demonstration of strain capability indicates that the CNTembedment method of the present application has the potential to be usedat any convenient location on the outer skins and spars of large scaleUAVs. Testing shows the embedded system of FIGS. 1 and 2 is capable of+5000,−4000 micro-strains which is a typical strain range for aircraftskins and spars at ultimate load during maximum pull-up deflection.

An article containing embedded CNT conductors was also tested todetermine signal integrity and power capability. FIG. 3 is a graphillustrating how embedded CNT signal performance is consistent withtraditional copper harnessing for serial and 10 Mbit Ethernet systems.The signal waveforms were generated for serial, MIL-STD-1553, and 10Mbit Ethernet interfaces using a 25 MHz signal generator. Signal testingshows no appreciable deviation under loading. Consistent signalperformance with copper harnesses was observed up to 25 MHz for squarewave input. Power testing was accomplished with a current control DCpower supply and temperature sensors on the test article. Non-linearchanges in current and temperature which would indicate a breakdown inthe conductor or failure of the conductive epoxy were not observed.Because of the high resistivity, the CNT conductors are ideal for signaland lower power applications. Essentially, the embedded CNTs have provento be as electrically conductive and reliable as a copper equivalent,without the deficiencies inherent to copper metal described above. At100 kHz, the square wave output signal was virtually identical to theinput signal, such that, when overlapped, the signals matched.Similarly, at 12.5 MHz, the output wave form was practically unchangedfrom the input signal, just shifted in the time domain.

Based on the developed conductor embedding methods and their successfulresults, this novel system and architecture will be a criticalenhancement to future vehicular electrical systems. For example, withoutembeddable harnessing, it is very difficult to reliably embed straingauges, constant voltage anemometers, temperature sensors, and otherhealth management systems directly into composite structures. Withembeddable harnessing, these sensors and networks can lead to new waysof maintaining up-to-date knowledge of airframe health, leading toenhanced preventive maintenance and system prognostics. In addition,decentralized control and aero-sensing systems can now be implemented aspart of a Fly-By-Feel and UAV system that does not suffer from the CTEmismatch and material degradation of copper systems, leading to morereliable system performance.

FIG. 4 depicts a ten-foot section 400 of a typical aircraft wing (e.g.,Aurora's Orion UAV). Several signal and/or power wire harnesses may beembedded in the wing area, such as engine harness controls, discretes(“kill”, “safe”), accelerometers, strain sensors, and constant velocityanemometers. For example, one or more sensors may be embedded in thewing panel 410 while the CNT conductors may be installed along theleading edge 402 and main 404 spars. In certain aspects, a sensor andits leads may be sandwiched between layers of PEKK. The versatility ofembedded harnesses enables embedding in and around the various ribs 408,412 and spars 402, 404, as well as other wing structures (e.g., bodypanels and skins).

With embedded CNT technology, a number of sensors and their associatedwiring may be installed on nearly any assessable surface of an aircraft.For example, one or more sensors may be provided throughout the vehicleto monitor/measure temperature and/or stress. Thermistors, a type ofresistor whose resistance varies significantly with temperature, may beemployed as an embedded temperature sensor since thermistors can be highresistance and do not require a metallic lead set. The thermistor's highresistance (e.g., 10,000Ω) reduces the error generated by the resistanceof the nanomaterial lead set and reduces error due to mismatch betweenthe two sides of the lead-set. A strain gage may be used to measurestress imparted upon the composite structure, such as foil-type straingages, which are available from OMEGA Engineering Inc. Generallyspeaking, a strain gage is a sensor whose resistance varies with appliedforce by converting force, pressure, tension, weight, etc., into achange in electrical resistance which can then be measured andcommunicated to a health monitoring system. In order to minimize thethickness that the embedded sensors add to the composite structure, theyare embedded within the composite structure wherein NiCVD material (insheet form) was chosen to be the electrical lead from the sensor tooutside of the composite structure. The NiCVD sheet leads may besoldered or adhered (e.g., conductive silver epoxy) to the sensors, butsoldering is generally faster, cleaner, and obviates the need to waitfor epoxy to cure. Testing indicated that encapsulated thermistors andstrain gages are still functional after being vacuum bagged and cured to250° F.

As with typical harness design, embedded harness design starts with alogical signal model and follows the definitions of a traditionalelectrical harnessing design rules. Indeed, the physical electricalembedded harness design is a cross-disciplinary activity involving bothelectrical and mechanical considerations. The task encompasseselectrical definition of the wire gauge for proper sizing of power andsignal lines using modeling of electrical characteristics cablecapacitance effect, and shielding from noise EMC/EMI. Otherconsiderations include resistance to environmental conditions andhazards, manufacturability, repair and maintainability, weight, andspace saving. Generally speaking, based on existing CNT technology, thecorrelation between CNT and copper wire is based on weight. For example,at DC, CNT is generally twice as heavy as copper. However, at about 15kHZ, CNT is more weight efficient than copper (not counting packaging).Moreover, volumetrically, the ratio of CNT to copper is approximately50:1. Currently, due to size constraints, CNT is more useful as a signalcarrier than a power carrier; however, may also be used to carry powerprovided there is space for the CNT.

Resistive Heating. The above-described embedded conductors may furtherfunction as embedded heaters to perform de-icing and/or anti-icingfunctions, while also keeping the temperature of the composite withinoperational limits without requiring protective metal components. Thatis, the embedded conductors may be used to produce an embedded heatermat that is more durable than traditional heater mats. Moreover, asdiscussed above, the embedded heater mat preferably utilizes acompatible resin system and may be galvanically and thermally matched tothe structural composite material (e.g., an aircraft's compositestructure). Indeed, a heater mat may be constructed from conductors insheet form (e.g., sheet, veil, etc.) and/or in cable form (e.g., yarns),which may be laid up in or with a composite structure using theabove-described methods.

While embedded conductors were found to generate heat when transferringpower from a source to a load, the amount of heat may be increased byconnecting one or more of the embedded conductor across the terminals ofa power supply such that the conductor becomes the load, therebyfunctioning as a resistor. For example, the one or more of the embeddedconductors may be coupled between the power supply's positive terminaland negative terminal.

The power supply, or similar device, may be adjustable so as to controlthe amount of power being provided to the embedded conductors.Generally, the higher the power, the greater the temperature generatedby the embedded conductor. To that end, a heater control system may beemployed to automatically, or dynamically, control and monitor theembedded conductors. For example, using temperature sensors (e.g., theembedded temperature sensors), the heater control system may monitor thetemperature of the heater mat to ensure that the temperature does notexceed a predetermined maximum value (e.g., the composite material'smaximum temperature), wherein the power to the heater mat may bedecreased or shut off if the temperature meets a predetermined warningthreshold temperatures (e.g., an amount less than the predeterminedmaximum value). Similarly, the heater control system may be configure tokeep the temperature of the heater mat at a particular temperature, orwithin a predetermined range of said particular temperature (e.g.,permitting for certain temperature deviation).

In operation, the heater mat may be designed to cover a wide-area of avehicle by dispersing the embedded conductors across a larger surface ofa specific composite component, thus creating a wide-area heater mat.For example, when used on an aircraft, the embedded conductors may bearranged to cover a larger portion of a wing (e.g., the topside,underside, etc.), flight control surfaces (e.g., flaps, ailerons, etc.),fuselage, and the like. The wide-area heater mat may then be heated to apredetermined temperature using a power supply or other deviceconfigured to output electric current (e.g., using the embeddedconductor(s) as a load). To tailor the power profile of the wide-areaheater mat, the conductive materials, or layup may be customized so asto direct (i.e., concentrate) the heat to a specific area of a wide-areaheater mats. For example, the orientation of plys and geometry relativeto the flow of electricity may be configured to increase or decreaseheat loading in specific areas as required per application. That is, toconcentrate heat at the nose of the leading edge, additional conductivematerial may be provided at the leading edge heater; that is, theportion of the embedded conductor at the nose may be larger, oradditional conductors may be provided. Moreover, layering of varyingconductive material types or of varying aerial weights may be used tocreate custom heat profiles/signatures. For example, additionalconductive material (e.g., a strip of very light weight non-woven carbonveil) may be added to a targeted region of the heater (e.g., a nose ofthe leading edge of a wing).

Providing additional conductive material at the targeted region lowersthe resistance of the targeted region, effectively funneling power tothe targeted region, thereby increasing the temperature of the targetedregion relative to the other regions (non-targeted regions) of theheater pad. Thus, an operator is able to customize the heat profile of asurface by selectively turning what was a cold area into a slightlyhotter area. Increasing the temperature at, for example, the leadingedge of a flight surface (e.g., a wing) would be beneficial as it wouldbetter split off the built up ice at the stagnation point on the nose ofthe leading edge. That is, as discussed with regard to FIGS. 7 a through7 c, the slightly hotter area may be a center strip (i.e., a long narrowstrip) designed to splice an ice sheet at the leading edge.

Varying the resistance across a wide-area heater to generate acustomized heat profile on the wide-area heater in particularadvantageous where only one power input/output is available, butdifferent areas of a structure or component have different temperaturesrequirements. In certain aspects, the embedded conductors of a wide-areaheater may be provided as a plurality of separately controlled circuits.For example, a first area circuit may be driven with a first powervalue, thus generating a first temperature, while a second area circuitmay be driven with a second power value, thus generating a secondtemperature. Further, such circuits may be switch controlled. Forexample, a wide-area heater may be configured with a plurality of switchcontrolled regions driven by a single power value, whereby one or moreof the plurality of switch controlled regions of the wide-area heatermay be selectively powered (e.g., activated/heated), by activating aswitching device to direct power to a particular region.

In certain aspects, one or more heater mats (or wide-areas heater mats)may be provided on a surface wherein the heater control system may beconfigured to dynamically and independently control the various mats, soas to only supply power (or portion thereof) to the heater matspositioned in areas that are in need of heating, thus reducingunnecessary power consumption.

To test the usability of the embedded heater mat as de-icing and/oranti-icing devices, two flat panel embedded heater mat test articleswere fabricated and tested. One test article used CNT materialconductors (i.e., heater strips), while the second test article usedNiCVD material conductors for heater strips. The CNT panel used threestrips of CNT that were 14 by 2 inches with 1- by 2-inch NiCVD strips onthe ingress/egress sites. One strip measured 3.5 ohms while the othertwo measured 3.0 ohms. The strips were also checked for any conductivitybetween each other. None was found. The NiCVD test panel used NiCVDstrips of the same dimensions, but with additional 1- by 2-inch stripsat the ingress-egress sites. The addition of embedded temperature andstrain sensors added some ridges to the core side of the article, butthe outside surface of the test articles remained smooth, which is idealfor the wing leading edge test article. The resistances of the heaterstrips were measured using a multimeter.

The heater strips were tested by applying current at the ingress-egresssights. Up to 3 amps were supplied to the heater strips, at which pointthe CNT strips were measured at approximately 200° F. with no sign ofsmoke. In using an IR camera to view the uniformity of heating throughthe heater strip, high concentrations of heat were noticed near theingress-egress sights when connecting using only alligator clips,however providing an electrical connector (e.g., metal) in between theingress-egress and the alligator strips allowed for a betterdistribution of the heat at the point of contact.

The tested heater strips were encased using the following layuparrangement: a film adhesive/PEKK/film adhesive barrier and embedded onone ply of fiberglass with two plys of carbon pre-preg on top of theheater strips, 0.25-inch-thick core, and finally two plys of carbonpre-preg. The ingress-egress sites were loose from the compositestructure to allow for alligator clamps to be connected for resistancemeasurements and for current to be applied. The resistance was measurefor the individual heater strips, as well as the heater strips in aparallel. In summary, the results indicated that CNT exhibited a lowerresistance, while placing the conductor in parallel reduced overallresistance.

An IR camera was used while applying current to the embedded heaterpanels. The camera allowed for local temperature measurements that couldbe compared to the thermocouples that were bonded to the outsidesurfaces of the panels in line with the heater strips. The images alsoshow the variance across the heater strips for a given amount of currentbeing applied. While the NiCVD heater strips require more power toachieve the same heater strip temperature, a forward looking infrared(“FLIR”) systems image comparison of the IR photographs of the CNT &NiCVD heaters during testing indicates that NiCVD heater strips tend tohave a more consistent heating along the length of the heater strip, aswell as fewer hot spots at the ingress-egress sites. Moreover, theeffectiveness of the core as an insulator is evidenced by FIGS. 5 and 6,which show the temperature difference between the outside surface (i.e.,the heater surface) and the inside surface for both the CNT and NiCVDheater strips. Specifically, FIG. 5 is a graph illustrating an exampleCNT embedded heater test panel temperature rising overtime while FIG. 6is a graph illustrating an example NiCVD embedded heater test paneltemperature rising overtime.

The embedded heater panels may be applied to a wing's leading edge 700.Accordingly, a test multi-functional wing 700 was designed asillustrated in FIGS. 7 a through 7 c. The multi-functional wing 700employed a CSA 702 having CNT yarns as signal wires, NiCVD sheets aspower cables, and carbon veil as the heater elements with thesurrounding composite structure. The multi-functional wing 700 furtherinclude a leading edge and supporting structure section having embeddedsensors, harness and heater elements. By highly insulating the corematerial, heat transfer to the interior of the airfoil may beprohibited. The airfoil leading edge was modeled as a cylinder, andstandard forced convection heat transfer correlations were used toestablish a heat flux boundary condition at the wing surface.

As noted above, additional conductive material may be provided at theleading edge of a multi-functional wing 700 in the form of a centerstrip 704 (i.e., a long narrow strip). The center strip 704 may beheated so as to split off any built up ice at the stagnation point onthe nose of the leading edge. That is, the center strip 704 may bedesigned to heat and splice an ice sheet at the leading edge, therebycausing the ice to separate from the surface of the wing surface andfall away from the aircraft. Thus, during the leading edge layup, acenter strip 704 may be placed in the very nose of the article. Further,such localized heating would be particularly useful when used inconnection with an electro expulsive de-icing system (EEDS) having anelectromechanical “thumper” to tap the nacelle from the inside to shedice.

The model was configured to evaluate the effect of the fiberglass layerand ice layer thickness on the heat input requirement to achieve atemperature of 100° F. on the external surface of fiberglass layer(i.e., skin). A cylindrical geometry, approximating the wing leadingedge test section, was assumed whereby the cylinder diameter was set at6 inches and the overall length was set at 8 feet. Preliminary thermalmodel results are shown in FIGS. 8 a and 8 b. FIG. 8 a plots thefiberglass skin temperature as a function of the CNT heat input forvarious fiberglass layer thicknesses assuming no ice layer is present.In this case, the skin surface temperature did not vary with thefiberglass thickness because it was assumed that the convective thermalresistance was constant and that no heat left the system through theinterior.

The results illustrated that a heat input of approximately 2.2 kW wasrequired to provide a skin temperature of 100° F.; on a surface areabasis this worked out to be about 3.8 kW/m². At this power inputcondition the temperature at the interface between the CNT and thefiberglass was calculated at approximately 130° F. assuming a fiberglasslayer thickness of 0.05 inch. Increasing the thickness of the fiberglasslayer to 0.1 inch also increased the interface temperature (to 158° F.).Prior studies have established the maximum allowable interfacetemperature at about 200° F. as above this temperature the layup maybegin to delaminate; this places a limit on the maximum allowable skinthickness for the layup. FIG. 8 b plots the skin temperature assuming anice layer is present on the external surface of the fiberglass layer,which is fixed at 0.05-in thick. The ice layer thickness was varied from0.04 to 0.40 inch to represent the range of ice layer thicknesstypically encountered in flight. As in the prior analysis, a 100° F.skin temperature was defined as the objective condition of the analysis;however, lower temperatures may be acceptable in a de-icing application.It should be noted that phase change effects due to melting of the icelayer were not considered in the analysis. The results illustrated thatthe ice layer acts as an insulator dropping the heat input requirementto reach 100° F. with increasing ice thickness. At an ice thickness of0.04 inch, the heat requirement is essentially the same as in the no icecase (2.2 kW), but at an ice thickness of 0.4 inch, the heat inputrequirement drops to about 1.6 kW (or about 2.7 kW/m²). FIGS. 8 a and 8b depict the fiberglass surface temperature as a function of heat inputthrough the CNT. The graph of FIG. 8 a varies skin thickness with no icelayer and the graph of FIG. 8 b varies ice thickness using a 0.05-inchfiberglass layer. The heat transfer analysis provided an initialestimate of the heat requirement for the airfoil de-icing/anti-icingsystem at between 2.7 and 3.8 kW/m².

As discussed above, ingress-egress may be accomplished using a PCBelectrical connector electrically bonded to pad sites for signal cabling(e.g., 4 signal wires and 2 power wires). An alternative electricalconnector may be a wire inserted directly into the layup. A benefit ofthis electrical connector is that it is simple to implement while alsoproviding sufficient current distribution at the ingress-egress pointssuch that not “hot spots” were created. Initial tests investigated usingvarious wire gauge sizes to carry the same current ranging from a single22 AWG wire to four 28 AWG wires. Wires were soldered to 40 gsm carbonveil with NiCVD pads. Multiple wires allowed better current distributionover the pad site and although were of greater number then a single 22AWG wire, they were easier to solder and required less solder overall.However, because larger single wires may be required, a compromise wasfound by stripping the 22 AWG wire and unwinding and splaying (i.e.,fanning) the individual copper strands. This was tested in two methods,one in which the copper strands were then bundled into 3 smaller pairsand one in which they remained individual splayed apart. The fanned outwires provided the same ease of soldering as well as currentdistribution at the pad site as the multiple wire configuration. Usingminimal amounts of solder is beneficial as it reduced the risk of solderbuild up resulting in peaks that could protrude through glass isolationplys resulting in shorting to carbon laminate. For these reasons,ingress-egress testing used splayed out 22 AWG wire.

Eleven coupons were created all of identical geometry, but varied NiCVDpad layers, soldering, and wire strand configuration. Four plys ofcarbon pre-preg were used for the base material. A switch from CNT toNiCVD material was made because it was provided a better resistancematch for the application. The available variability of NiCVD materialand low cost makes NiCVD material extremely attractive for resistiveheater applications. Additionally, NiCVD material's light weight andthinness make it relatively easy to incorporate into existing structuraldesigns without impacting appearance and performance of the surroundingstructure. FIG. 9 shows the configurations tested.

The basic conclusion from these tests was that the NiCVD material padmay not be necessary to distribute the current at the ingress-egresspoint when splayed wires are employed as they yielded a significantimprovement over bare stripped single wire bundle. Thus, a configurationusing a splayed wire directly on top of the carbon veil conductor, nosolder, and no NiCVD pad may be employed.

An example configuration for facilitating proper electrical isolationbetween the CNT heater strips and the surrounding carbon structure isillustrated in FIG. 10, which was configured to ensure that the heaterstrips (i.e., the various conductors/resistors) are electronicallyisolated from the surrounding composite structure.

The individual components shown in outline or designated by blocks inthe attached drawings are all well-known in the electrical conductanceand aviation arts, and their specific construction and operation are notcritical to the operation or best mode for carrying out the invention.While the description so far has centered on use in aviation, it isclear to those of skill in the art that it can equally be applied toother vehicles and vehicular systems, including, for example,automobiles, motorcycles, trains, ships, boats, spacecraft, andaircraft.

While the present embedded conductor harness technology is generallydescribed in the context of aerial vehicles, other composite structuresmay similarly benefit from embedded conductor harness technology, suchas automobiles, watercraft, windmill blades, helicopter blades, etc.Further, while the present invention has been described with respect towhat are presently considered to be the preferred embodiments, it is tobe understood that the invention is not limited to the disclosedembodiments. To the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

All U.S. and foreign patent documents, all articles, brochures, and allother published documents discussed above are hereby incorporated byreference into the Detailed Description of the Preferred Embodiment.

What is claimed is:
 1. A multi-functional composite system, themulti-functional composite system comprising: a core; a plurality ofstructural composite fiber layers; a matrix material; a compositeconductor assembly, the composite conductor assembly having one or moreconductors disposed between two or more insulating layers, an electricpower source electronically coupled with said composite conductorassembly, the electric power source is configured to pass electriccurrent through at least one of said one or more conductors.
 2. Themulti-functional composite system of claim 1, wherein at least one ofsaid one or more conductors is electrically coupled across the electricpower source's positive terminal and negative terminal to function as aresistive load.
 3. The multi-functional composite system of claim 2,wherein said at least one of said one or more conductors generates heatwhen electric current is passed through said at least one of said one ormore conductors.
 4. The multi-functional composite system of claim 3,wherein said at least one of said one or more conductors generates heatfor de-icing or anti-icing the composite structure.
 5. Themulti-functional composite system of claim 3, wherein the one or moreconductors are arranged to yield a wide area heater mat having apredetermined heat profile.
 6. The multi-functional composite system ofclaim 3, wherein the predetermined heat profile is accomplished bydirecting heat to a targeted region.
 7. The multi-functional compositesystem of claim 6, wherein the targeted region a flight surface'sleading edge.
 8. The multi-functional composite system of claim 6,wherein heat is directed to a targeted region by reducing the resistanceof a conductor, or portion thereof, positioned at the targeted region.9. The multi-functional composite system of claim 8, wherein theresistance of the conductor is reduced by increasing the amount ofconductive material at the targeted region.
 10. The multi-functionalcomposite system of claim 6, wherein heat is directed to a targetedregion by configuring the orientation and geometry of the one or moreconductors relative to the flow of electricity.
 11. The multi-functionalcomposite system of claim 1, wherein the composite conductor assemblycomprises a first and a second conductor, which are independentlycontrolled such that the electric power source selectively passeselectric current through the first or the second conductor.
 12. Themulti-functional composite system of claim 1, wherein at least one ofsaid one or more conductors comprises a carbon nanotube material or anickel chemical vapor deposition material.
 13. The multi-functionalcomposite system of claim 1, wherein at least one of said one or moreconductors ingresses or egresses the multi-functional composite systemwhile maintaining electrical isolation between the composite structureand the one or more conductors.
 14. The multi-functional compositesystem of claim 1, wherein the composite conductor assembly, theplurality of structural composite fiber layers, and the matrix materialare galvanically or thermally similar.
 15. The multi-functionalcomposite system of claim 1, wherein the composite conductor assemblyfurther comprises a shielding material.
 16. The multi-functionalcomposite system of claim 1, wherein at least one of said one or moreinsulating layers comprises Poly Ether Ketone Ketone or etched, bondablepolytetrafluoroethylene.
 17. A heater assembly for embedment in acomposite aircraft component, the heater assembly comprising: aplurality of conductors disposed between two or more sheets ofinsulating layers; an adhesive resin bonding the plurality of conductorsand the two sheets of insulating layers into a heater assembly such that(i) the conductors are electrically isolated and (ii) structural loadscan be passed through said heater assembly; and two or more electricalconnectors electronically coupled to one or more of said plurality ofconductors, the two or more electrical connectors being configured suchthat electric current may be applied across said one or more of saidplurality of conductors causing said one or more of said plurality ofconductors function as a resistive load, thereby generating heat forde-icing or anti-icing the aircraft component.
 18. The heater assemblyof claim 17, wherein at least one of said plurality of conductorscomprises a carbon nanotube material or a nickel chemical vapordeposition material.
 19. The heater assembly of claim 17, wherein theplurality of conductors are arranged to yield a wide area heater mat,whereby heat is directed to a targeted region of the wide area heatermat.
 20. The heater assembly of claim 19, wherein the targeted region aflight surface's leading edge.
 21. The heater assembly of claim 19,wherein heat is directed to the targeted region by reducing theresistance of a conductor, or portion thereof, positioned at thetargeted region.
 22. The heater assembly of claim 21, wherein theresistance of the conductor is reduced by increasing the amount ofconductive material at the targeted region.
 23. The heater assembly ofclaim 21, wherein said one or more conductors and said two or moreinsulating layers are provided using a fiber metal laminate material.24. A method for heating an aircraft's load-bearing composite structure,comprising the steps of: forming a composite conductor assembly having(i) one or more conductors disposed between two sheets of insulatinglayers, and (ii) an adhesive resin bonding the one or more conductorsand the two sheets of insulating layers such that the one or moreconductors are electrically isolated from each other and from anyaircraft structural member, and such that structural loads can be passedthrough said conductor sandwich assembly; and bonding the compositeconductor assembly to the aircraft's load-bearing composite structure,the load-bearing composite structure having (i) a core, (ii) a pluralityof structural composite fiber layers, and (iii) a matrix material; andelectrically coupling the composite conductor assembly with an electricpower source, wherein at least one of said one or more conductors iselectrically coupled across the electric power source's positiveterminal and negative terminal to function as a resistive load, whereinthe electric power source is configured to pass electric current throughat least one of said one or more conductors, and wherein said at leastone of said one or more conductors generates heat when electric currentis passed through said at least one of said one or more conductors. 25.The method of claim 24, wherein said at least one of said one or moreconductors generates heat for de-icing or anti-icing the aircraft'sload-bearing composite structure.